1. Field of the Invention
The present invention relates to a method of converting color data from four or more color device data, e.g., device data C, M, Y, K into device data C, M, Y, K under different output conditions.
2. Description of the Related Art
Image output devices for outputting a color image on an output medium such as a printed material or a CRT achieve halftone dot area modulation or density modulation on the output medium based on device data C, M, Y, K or R, G, B to reproduce a color image. Color characteristics of the reproduced color image depend on output conditions including the properties of color materials and output medium, e.g., an output sheet, phosphors, etc. and other printing conditions.
There have been proposed various methods for determining device data to obtain desired color images in view of such output conditions. For example, Japanese laid-open patent publication No. 3-131920 discloses a process of carrying out direct mapping using a color conversion table determined with a certain printer or under certain printing conditions to determine device data. Japanese laid-open patent publication No. 4-362869 reveals a process of determining a solution of maximum likelihood for the coefficient of a masking process such that colorimetric values of different image output devices will be equalized, and obtaining device data using the determined coefficient.
An image output device for producing a colored printed material is desired to produce variations of an image to be outputted. For example, the image output device is required to select a color material and an output medium, and adjust the amount of the selected color material to obtain a desired image. The conventional processes described above, however, fail to carry out highly accurate color conversions to meet such a requirement.
For generating a color printed material, it is customary to use four colors C, M, Y, K as device data. In order to map device data C, M, Y, K of a source device into device data Cxe2x80x2, Mxe2x80x2, Yxe2x80x2, Kxe2x80x2 of a destination device under different output conditions, it is necessary to convert the device data C, M, Y, K into device-independent colorimetric values L*, a*, b*, and then convert the calorimetric values L*, a*, b*, into the device data Cxe2x80x2, Mxe2x80x2, Yxe2x80x2, Kxe2x80x2. Since the device data Cxe2x80x2, Mxe2x80x2, Yxe2x80x2, Kxe2x80x2 comprise four variables whereas the colorimetric values L*, a*, b* comprise three variables, accurate conversion relationships cannot be attained by the above conventional processes. For generating a printed material, in particular, conversion relationships need to be established so as to preserve an attentional color such as of gray and reduce the sacrifice of other colors. It is the current practice to set up such conversion relationships with a large expenditure of time and labor.
It is a general object of the present invention to provide a method of converting color data very easily between sets of four or more device data under different output conditions to obtain desired colors.
A major object of the present invention is to provide a method of converting color data very easily between sets of four or more device data under different output conditions while preserving a gray balance to obtain desired colors with a preserved gray balance.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.